This invention relates to two component, epoxy resin systems curable at room temperatures, and more specifically to compositions of the mutually reactive epoxy resin and hardener components, as employed in particular mastic, or putty formulations, where the two components are packaged in close side by side relationship, in the form of bars or tapes. Further, the invention relates to shelf stable, plural component, epoxy resin systems, in a mastic, palpable form, suitable for convenient mixing, by hand or machine means, and, after mixing, curable to a solid state in a short time, without the application of external heat.
Epoxy resins can be cured under room temperature conditions, by admixture with a wide variety of chemicals that are capable of opening the oxirane ring, and developing a polymeric structure. Such curing agents are well known, and the stochiometry for optimum concentrations well established in the patent literature, text books, and numerous articles. The subject of curing agents is comprehensively dealt with in, "Handbook of Epoxy Resins" by Lee and Neville, McGraw-Hill Company, Chapters 5 to 12 inclusive.
From a practical view point, however, in the commercial or consumer market for room temperature curing epoxy systems, in the form of palpable mastics, a number of critical factors affect the decisions as to the composition of the systems. In particular, such factors are important when the mastic is designed for probable hand mixing, and is in the form of bars or tapes, in close side by side relationship, confined in a closed container, and/or packaged upon or between film.
Because of the practical desirability of polymerization at ambient temperatures after mixing, it is required that a high degree of mutual reactivity be maintained prior to and during polymerization. High molecular weight epoxy resins, or amine hardeners, generally have less reactive sites than lower molecular weight materials, and are thereby very slow to cure without supplemental heat. Traditionally, practical materials for the cure of epoxy resins at room temperature have been aliphatic, or alicyclic primary diamines, either alone, adducted with epoxy resin, or converted to fatty acid amines by condensation, cyanoethylated, or by other chemical modifications. Lewis acids, or Friedal Craft type catalysts, and adducts as a large class of compounds, can be utilized to cure epoxy resins at ambient temperature, as can some polymeric mercaptans.
Selection of a practical curing agent for a hand mixable, room temperature cure mastic, package in a common environment, requires careful consideration of a number of the properties of the system for commercial practicality, such as:
(a) The unmixed components must have long shelf life in close side by side relationship, sharing the same environment.
(b) Since contact with the bare hands during mixing, or placement of the mixed compound, is typical; any toxicity, irritation potential, sensitization, and offensive odor must be avoided.
(c) After mixing, the mastic must be capable of an application time between several minutes to several hours, and a setup or hardening time of less than eight hours, at ambient temperature.
(d) No staining, and easy removal from the hands are both required.
Presently marketed epoxy mastic systems, with surfaces of the two components exposed to a mutual environment, have a limited shelf life, particularly when exposed to higher temperatures during shipping, and due to poor storage conditions. The curing agent normally employed is based on the aliphatic diamines, and usually is a fatty acid polyamide such as a Genamid or Versamid type, as manufactured by General Mills. Hardeners of these lower molecular weight, liquid, aliphatic, or alicyclic types, release either ammonia, or chemically active amine type vapors, which permeate the common environment of the package, and cause progressive hardening of the epoxy component, which eventually makes mixing extremely difficult, or impossible.
A further problem has to do with the fact that amines with an appreciable vapor pressure, when exposed to air will readily absorb carbon dioxide to form amine carbonates, which are solids, and tend to harden the curing agent to form an unusable mastic.